PCB breakdown in rivers depends on sediment-specific bacteria

One of Mother Nature’s most promising weapons to break down persistent, toxic polychlorinated biphenyls (PCBs) is bacteria. Now, a study by Carnegie Mellon University scientists provides convincing evidence that how quickly a PCB gets eaten and what it becomes depends on where it settles. Using DNA fingerprinting, the Carnegie Mellon team discovered distinct bacterial populations in the first-ever side-by-side comparison of PCB-laden sediments taken from separate, contaminated rivers. The results are being reported by graduate student Christine Wang on Sunday, Aug. 22, at the 228th annual meeting of the American Chemical Society (ACS) in Philadelphia, Pa. (ENVR 12, Loews -- Commonwealth B).

The investigators studied sediments taken from two rivers in upstate New York where local industries had released PCBs over several decades. They found that bacteria in contaminated Hudson River sediment were faster at digesting an introduced PCB compared with sluggish bacterial cousins at work in contaminated Grasse River sediment.

"Our goal is to determine the roles that different bacterial populations play in PCB breakdown by identifying the kinds of microbes in river sediments as well as their population size and how they remove chlorine atoms from the PCB structure," said William Brown, Ph.D., professor of biological sciences and a principal investigator on the study. "This work tells us that PCB-digesting microbes need to be examined in each contaminated lake or river to understand the fate of PCBs at different sites."

Co-investigators on the team include Edwin Minkley, director, Center for Biotechnology and Environmental Processes in the Department of Biological Sciences, and Jeanne VanBriesen, assistant professor of civil and environmental engineering.

The team is exploring whether different nutrients or other factors could account for the variation between PCB-digesting microbial communities taken from the two rivers.

The research team ultimately hopes to coax bacteria with a preference for PCBs into becoming more dominant life-forms in sediments. Future studies that modify nutrients in sediments from contaminated sites with little or no bacterial activity also could reveal ways to transform sites with poor eaters into areas that grow microbes with healthy appetites for PCBs.

Ideally, the investigators could identify a combination of nutrients or other factors that could be added to river sediments to accelerate the breakdown of PCBs in situ, without having to dredge a river. Should dredging be needed, their research also could identify ways to break down PCBs in sediments that are disposed in secure, hazardous waste landfills. Ultimately, the team’s work could result in approaches that detoxify PCBs much more thoroughly and much faster than any existing method.

While other studies have shown that unique populations of PCB-digesting microbes inhabit different waterways, the investigators believe that this is the first side-by-side comparison of populations using the same experimental approaches under identical conditions.
Despite 30 years of scientific investigation and search for remediation approaches, the contamination of waterways with PCBs remains a pressing environmental challenge. A mixture of 209 related chemicals, PCBs accumulate in fish and birds high in the food chain, crippling their ability to reproduce. These agents also build up in humans, where they are suspected of harming reproduction, causing cancer, injuring the immune system and thyroid gland, and impairing learning and memory.

PCBs were generated worldwide largely by industries that manufactured plastics, paints, lubricants, transformers and other materials. In the mid-20th century, companies along the Hudson and other rivers in upstate New York collectively released more than one million pounds of PCBs into the water, not knowing that these pollutants could linger for thousands of years. While U.S. production ceased in 1978, PCBs continue to endanger waterways across the United States from historic and ongoing uncontrolled releases.

This research is part of a large-scale, interdisciplinary project funded by the Packard Foundation to understand the environmental fate and persistence of PCBs. The project, "Effects of Sediment Biogeochemistry on the Environmental Fate and Persistence of Polychlorinated Biphenyls," is led by David Dzombak, professor of civil and environmental engineering at Carnegie Mellon. This work is being presented as part of a multi-institutional ACS meeting symposium, "PCBs in Freshwater and Marine Sediments: Transport, Transformation, and Treatment," organized by Dzombak and colleague Greg Lowry, assistant professor of civil and environmental engineering.

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